Skeletal muscle atrophy and weakness affects nearly all of the nation's elderly and often leads to frailty, immobility, falls, fractures, and institutionalization. Numerous studies have shown that weight training involving Shortening Contraction Training (SCT) protocols can slow or even reverse this decline. Unfortunately, traditional SCT protocols commonly have low trainee compliance and can be too strenuous for many older individuals. On the positive side, recent studies show that even greater strength increases can be safely realized via Lengthening Contraction Training (LCT) which incurs a lower acute metabolic cost and results in lower rates of perceived exertion than SCT. Consequently, LCT is a particularly attractive intervention for the elderly, energetically impaired, and less athletically-motivated populations. Despite these advantages, no commercially available system exists for LCT. Therefore, during Phase I of this research project, Bio Logic Engineering, Inc. will develop an innovative computer controlled and motorized prototype to enable safe and effective weight training with advanced SCT and LCT protocols on a leg press machine. The system will be modular and adaptable to other types of stacked weight machines. Assessment of preliminary system performance will be conducted over a four week training period with two young healthy adults. The potential market for the proposed system is large considering its potential for training and assessment use in physical therapy clinics, assisted-living communities, hospitals, health clubs, recreational centers, academic institutions, and corporate wellness centers. System refinement and extensive human testing and hypothesis-based research will be conducted in Phase II.